Hard drives utilizing magnetic data storage disks are used extensively in the computer industry. Each magnetic data storage disk in a hard drive has an associated slider which carries a read/write head used to magnetically read and write data to and from the disk. During operation, the disks are rotating and one slider is maintained close to the surface of each disk or two sliders are close to the top and bottom surfaces of the disk respectively. The motion of the disk past the slider and the slider geometry, in particular the geometry of its surface facing the disk or the air bearing surface (ABS) regulates the flying height of the slider. Thus the distance between the disk and the read/write head are to be tightly controlled to improve data communication between the read/write head and the disk. This distance is called the flying height of the slider on the disk.
Typically, the slider is shaped to fly upon a cushion of air formed by the rapidly rotating disk surface between the air bearing surface and the disk surface. The air bearing surface has a shape which is designed to provide for a low but stable flying height between the slider and disk. The slider must not touch the disk surface because damage can result. Also, it is desirable to maintain as small a flying height as possible, because the closer the read/write head is to the disk surface the higher the areal density of data which can be stored on the disk. As flying height is reduced, it becomes increasingly difficult to maintain the flying height accuracy for a production population of sliders to the degree required for reliable recording and reading of data.
The shape of the slider has a substantial effect upon flying height. More specifically, the flying height is dependent upon the average curvature of the air bearing surface of the slider. The curvature of the air bearing surface is often affected by the manufacturing processes used to make the slider. Cutting, grinding and lapping operations in making the slider (either the air bearing surface or a surface opposite to the air bearing surface) often cause stress variations in the slider which distort the shape of the air bearing surface. After the final lapping, it is almost always necessary, especially for high storage density applications, to adjust the curvature of the air bearing surface to a desired target curvature. After the completion of the slider manufacturing process, a particular slider exhibits a combination of curvature properties. A population of sliders will exhibit a distribution of flatness parameters that can be described statistically. When the slider is bonded onto a head gimbal (HG) steel suspension, the flatness parameters are modified in an unpredictable manner. The distribution of curvature parameters associated with a population of sliders will be adversely affected by the bonding process of the HG assembly (HGA). For example, the mean of the flatness parameters will change and the standard deviations of the various flatness parameters will increase after HGA bonding. The causes include variations in the initial flatness, flexibility, surface stress and smoothness of the population of suspension arms, and variations in the epoxy uniformity and processing conditions.
The curvature of a slider is described by three parameters: crown curvature, camber curvature, and twist. Crown is the curvature along a direction parallel to the recording tracks of the data storage disks. Camber is the curvature along a direction perpendicular to the recording tracks. Twist is the curvature difference along the two diagonals of the slider as in the shape frequently present in a potato chip (two diagonal corners curved upwards, and two diagonal corners curved downwards).
U.S. Pat. No. 5,266,769 to Deshpande et al. discloses a method of adjusting the curvature of the air bearing surface of a slider by scribing a back surface (opposite the air bearing surface) of the slider. The scribing modifies the stress at the back surface, thereby controllably changing the curvature of the air bearing surface. Scribing may be performed with a laser, a sandblasting tool or the like. A curvature measuring tool may monitor the curvature of the air bearing surface as material is removed, thereby providing feedback control if desired. The method of Deshpande is effective for controllably changing the crown and camber curvature of the air bearing surface of the slider but ineffective in controlling the subsequent effects of the HGA bonding process mentioned above.
To better illustrate this shortcoming, FIG. 1 shows a portion of a head gimbal assembly 10. The assembly 10 has a slider 12 attached to a suspension arm 14. The suspension arm 14 is bonded to a mounting section 16 which attaches to a rotary actuator (not shown) inside a hard drive. The slider 12 has an air bearing surface 18 facing away from the suspension arm 14. The suspension arm 14 is made of a thin piece of flexible metal such as stainless steel. The slider 12 is attached to the suspension arm 14 with an adhesive such as epoxy.
A problem with the current state of the art is that the curvature of the air bearing surface 18 changes unpredictably when the slider 12 is attached (i.e. glued) to the suspension 14. Therefore, although slider curvature can be accurately adjusted using the method of Deshpande, a slider no longer has an accurately determined curvature after attachment to a suspension 14. This leads to imprecise flying height for the slider, resulting in an increased chance of drive failure and reduced data capacity.
U.S. Pat. No. 5,712,463 to Singh et al. discloses a method of adjusting the gram load applied to a slider and attitude of a slider attached to a suspension. The method includes the steps of scribing the suspension at certain hinge locations away from the slider so that the spring characteristics of the suspension are altered. The method disclosed by Singh is not capable of altering the curvature (e.g. crown or camber curvature) of a slider attached to the suspension. The method of Singh cannot change the shape of the slider. The method of Singh can only change the gram load applied to the slider and angular orientation (i.e. attitude) of the slider. Therefore, the method of Singh cannot solve the problems relating to slider curvature changes resulting from attachment to a suspension.
Yet another prior art approach to non-local processing of the flexure arm to which the slider is attached is described in U.S. Pat. No. 5,687,597 to Girard. Unfortunately, this method is very cumbersome and is not capable of accurately adjusting the crown, camber and twist of the slider's air bearing surface. Rather, this approach is aimed at adjusting the gram load of the suspension to solve for imprecisions in flying height and does not address changes to the slider's shape and air bearing surface after attachment to the suspension.
It would be an advance in the art of data storage drive construction to provide a method for adjusting the curvature of an air bearing surface of a slider after the slider is attached to a suspension such as an HGA. Such a method would provide increased control of slider curvature for sliders in data storage drives and lead to tighter flying height distributions and ability to store data at higher areal densities.